Known devices for valve clearance take-up have up until now above all been used specially for this purpose, that is the take-up of clearance, both so as to achieve a quieter running of the engine and to reduce the stresses therein. Such a device is known, for example, from GB-A-2 138 093.
The ever growing demands over the last few years for more effective auxiliary braking systems on commercial vehicles has led to ever more advanced solutions to satisfy the demands. One of these is described in Swedish patent application 8900517-7 (and WO-A-90/09514). According to this document the camshaft of the engine's valve system is used to obtain negative work from the engine instead of positive work which it is normally intended to achieve. This is achieved with the aid of extra lobes on the camshaft which open a connection between the engine's combustion chambers and its exhaust system during the latter portion of the inlet stroke (four-stroke motor) and by closing this connection at the first portion of the corresponding compression stroke. In this way, a large portion of the compression work is lost as braking. The said additional lobes on the camshaft are so small that in terms of size they fall into the category which can be called normal clearance in an engine of this type. Another engine-braking device is described in EP-A-0 269 605 in which valve clearance take up means are located in a recess in the cylinder-head of an internal combustion engine directly beneath the end of the rocker arm remote from the valve stem.
Known methods and devices for actively adjustable valve clearance take-up include separate systems for the activation and de-activation, controlled either by electrical systems or by separate hydraulic systems No matter which type is chosen, a relatively high grade of complexity is required, particularly with the implementation of a separate hydraulic system. In addition to the fact that this means almost a doubling of the number of hydraulic components in the valve system, a result thereof is the reduced reliability and a larger production cost per unit.